Commercial printed circuit cards are attractive because of their low cost, availability, and standard electrical and mechanical configuration. However, most electronic circuit boards are designed for use in fairly benign environments, such as inside a computer or television. Typically, heat transfer is by means of either forced or free convection, and there is no significant vibration.
For use in environments where convection is not available for heat transfer or where significant mechanical stress can be expected, it is necessary to enhance the thermal and dynamic characteristics of the printed circuit board.
A common technique for improving the thermal characteristics of a printed circuit board is the use of a heat sink to which heat is conducted. U.S. Pat. No. 4,731,698, U.S. Pat. No. 4,602,314, U.S. Pat. No. 4,468,717, U.S. Pat. No. 4,330,812, U.S. Pat. No. 3,631,325 discuss such techniques.
Stress on printed circuit boards has been controlled to some extent by means of limiting the board size or by using stiffeners. This raises the natural vibrational frequency of the board. U.S. Pat. No. 3,689,804 describes the use of a flexible layer between a circuit board and its housing to prevent cracking of the board or its circuits.
A problem with existing packaging techniques is that they are directed to either protection from heat or stress, but not both. A need exists for a circuit board packaging that performs both functions.